Centrifugal switch having a compression spring engageable with a radially movable brush and receivable on a cup-shaped shield upon movement of the brush



Sept. 14, 1965 H. o. MOORE 3,206,571

CENTRIFUGAL SWITCH HAVING A COMPRESSIQN SPRING ENGAGEABLE WITH A RADIALLY MOVABLE BRUSH AND RECEIVABLE ON A CUP-SHAPED SHIELD UPON MOVEMENT OF THE BRUSH Filed June 6, 1963 INVENTOR. HARRY O. MOORE ATTOE/VEV5 United States Patent 3,206,571 CENTRIFUGAL SWITCH HAVING A COMPRES- SION SPRING ENGAGEABLE WITH A RADIALLY MOVABLE BRUSH AND RECEIVABLE ON A CUP-SHAPED SHIELD UPON MOVEMENT OF THE BRUSH Harry 0. Moore, Charlotte, N.C., assignor of fifty percent to Frank E. Godley, Charlotte, N.C. Filed June 6, 1963, Ser. No. 286,008 1 Claim. (Cl. 200-80) This invention relates to an improved centrifugal switch particularly devised for breaking the circuit to the starting stator winding of capacitor and split-phase electric induction motors whenever the rotor thereof reaches a predetermined speed.

1 Various types of prior art centrifugal switches have been previously known which were intended to attain these same results. However, to my knowledge, all such prior art types of switches have required that metallic contact slip rings and brushes continuously move in relative sliding interengagement at all times during operation of the motor so as to insure that the starting winding would be effective during acceleration of the motor. Thus,the brushes and/ or slip rings would become worn beyond use quite rapidly and the brushes could not then be maintained in positive engagement with the slip rings.

It is therefore an object of this invention to provide a compact and efiicient centrifugal switch assembly adapted to be fixed on the rotor shaft of an electric motor and wherein stationary slip rings are provided to which electrical conductors may be permanently attached, and wherein a centrifugally operated conducting elementor brush is arranged to rotate with said shaft and relative to said slip rings and contacts the slip rings during only the acceleration and deceleration periods of the rotor,

thus greatly prolonging the useful life of the brush and slip rings as compared to the known prior art centrifugal switches.

It is a more specific object of this invention to provide a centrifugal switch assembly of the type described in which said stationary slip rings are fixed on a pair of insulation rings jour'naled on a sleeve adapted to be fixed on the rotor shaft of an electric motor, and wherein said sleeve has a pin extending radially therefrom, between the insulation rings and slip rings, and on which the centrifugally operated brush is loosely mounted, with spring means biasing the brush toward the slip rings.

It is still another object of this invention to provide a centrifugal switch assembly of the type last described including magnetic means operative in opposition to said spring means, for holding the brush out of contact with slip rings during rotation of the rotor shaft at speeds above a predetermined speed.

Some of the objects of the invention having been stated, other objects will appear as the description proceeds, when taken in connection with the accompanying drawings, in which- FIGURE 1 is a somwhat schematic perspective view of an electric motor showing the improved centrifugal which assembly mounted on the rotor shaft thereof;

FIGURE 2 is a schematic diagram of the electrical circuit associated with the electric motor and the centrifugal switch assembly shown in FIGURE 1;

FIGURE 3 is an enlarged fragmentary vertical sectional view taken substantially along line 3-3 in FIG- 3,206,571 Patented Sept. 14, 1965 FIGURE 5 is a fragmentary plan view, partially in section, taken along line 5-5 in FIGURE 3.

Referring more specifically to the drawings, the numeral 10 broadly designates an electric motor including a substantially cylindrically-shaped casing 11 which is shown broken away and partially in section in FIGURE 1. The motor 10 is a so-called induction motor and may be of the split-phase or capacitive type. Accordingly, casing 11 carries a starting stator winding 12 and a main or running stator winding 13, the windings 12, 13 being omitted in FIGURE 1, for purposes of clarity, but being shown schematically in FIGURE 2. Casing 11and its stator windings 12, 13, surround a rotor 14 provided with the usual inductors and which rotor is fixed on a rotor shaft 15.

As is well known, in the starting of a motor of the split-phase or capacitive type, the current is first supplied to both the starting and running stator windings and, when the motor speed increases to a predetermined maximum, the current to the starting stator winding is cut off. The present switch assembly, broadly designated at 20, is employed to supply current to the starting stator winding 12, to start the motor, and to cut the current off of winding 12 when the motor reaches a predetermined speed.

The centrifugal switch assembly 20 is mounted on rotor shaft 15 adjacent rotor 14 and, when rotor shaft 15 is at rest, the centrifugal switch assembly 20 normally establishes contact between a pair of conductors 21, 22: Conductor 21 is connected to a lead conductor 23 extending from one end of running stator winding 13 to one side of a suitable source of alternating current, not shown. The other end of running stator winding 13, and the corresponding end of the starting stator winding 12, are connected to a'lead conductor 24 which extends to the other side of the source of alternating current and which may have a suitable master switch 25 inter posed therein. Conductor 22 leads from the centrifugal switch assembly 20 to the end of the starting stator winding-12 opposite from lead conductor 24, and in the event that the motor is to be of the capacitive type, a suitable capacitor 26 may be interposed in' conductor 22.

As best shown in FIGURES 3 and 4, the centrifugal switch assembly 20 comprises a rotary part or sleeve 30, preferably formed of steel or thelike and which is shown in FIGURES 3 and 4 as being rigidly mounted upon rotor shaft 15 and which may be fixed on rotor shaft 15 by having a tight press fit thereon. Sleeve 30 is encircled by a pair of axially spaced contact or slip rings a, b which are journaled on and insulated from sleeve 30 by means of bearing members 31, 32 and correspond- URE 1, and showing the brush in active position against ing insulation rings '0, d. The bearing members 31, 32 are preferably in tubular form and are preferably made from compressed graphite or nylon or other suitable bearing material which will not require external lubrication.

The insulation rings 0, d are preferably'molded from a suitable plastic material, such as nylon or the like, and are loosely mounted on the respective bearing members 31, 32 so the bearing members 31, 32 and sleeve 30 may rotate freely relative to the insulation sleeves c, 11. Also, insulation rings c, d are integral parts of a switch housing broadly designated at 35 which, for purposes of assembly, is preferably formed of two substantially cupshaped halves which, upon being assembled, may be sealed together, as at 37, by a suitable thermoplastic material or suitable adhesive material. v

When assembled housing 35 includes, in addition to in: sulation rings 0, d, a pair of annular disk-like end walls 40, 41 and an interconnecting outer annular wall 42. Since housing 35 is preferably of molded construction, the two halves thereof and the insulation rings 0, d thereof may be molded partially around the metallic slip rings a, b. Also, corresponding end portions of the electrical conductors 21, 22 are molded in the walls 40, 41 of housing 35 and have their proximal ends welded or otherwise suitably permanently secured to slip rings a, b.

The conductors 21, 22 preferably extend substantially radially from slip rings a, b and through the walls 41), 41 of housing 35'. In order to limit axial movement of housing 35 relative to sleeve 30 and bearing members 31, 32, the opposed end portions of sleeve 30 have limiting collars 44, 45 pressed or otherwise suitably secured thereon and engaging the distal ends of the bearing members 31, 32.

The slip rings a, b may be restrained from rotation with sleeve 30 by any suitable means. In this instance, since slip rings a, b are secured or molded onto insulation rings c, d, the slip rings are restrained from rotation by means of a restraining arm 46 which is suitably secured to the annular outer wall 42 of housing 35, as by screws 47. Restraining arm 46 extends outwardly from housing 35 and may be suitably secured to the inner surface of motor casing 11, as by screws 48.

When rotor shaft and sleeve 30 are at rest or rotating at a relatively slow speed in the course of acceleration thereof, the slip rings a, b are engaged by opposed end portions of a metallic conducting element or brush 51. Brush 51 is preferably made from steel and slip rings a, b are preferably made from copper or brass, although the sleeve a, b and brush 51 may be made from any suitable conductive or metallic material.

In order to guide brush 51 for radial movement relative to slip rings a, b and to cause brush 51 to rotate with sleeve 30 and rotor shaft 15, so the brush 51 will be forced outwardly away from slip rings a, b by centrifugal force whenever said sleeve 30 and rotor shaft 15 exceed a predetermined minimum speed, a guide means is provided in the form of a shoulder screw or pin e whose inner end is threaded into an enlarged medial portion 30a of sleeve 30. Screw e extends radially outwardly between and in spaced relation from insulation rings 0, d and slip rings a, b and loosely extends through a medial portion of brush 51 and a thin insulation plate 53 adhesively or otherwise suitably secured to the outer surface of brush 51. It will be noted that brush 51 and insulation plate 53 have a bore 1 therethrough which is of substantially greater diameter than the diameter of screw or pin e to thereby insure that brush 51 and insulation plate 53 are free to move radially of slip rings a, b without being encumbered by pin e.

A permanent magnet 54 is adhesively or otherwise suitably secured to the outer surface of insulation plate 53 and is also loosely penetrated by the pin e.

The outer surface of permanent magnet 54 is engaged by the inner end of a compression spring 55 which loosely extends into a cup-shaped shield or metallic member 56 Whose outer wall is engaged by spring 55 and urged against the inner surface of the head g of screw e. The depth of cup-shaped shield 56 should be such that the entire spring 55 may be compressed therewithin as shown in FIGURE 4 when magnet 54 is in engagement with and being magnetically attracted to the inner portion or end of cup-shaped shield 56.

In operation, it is apparent that, when the rotor shaft 15 is at rest the brush 51 occupies the closed position shown in FIGURE 3 and maintains contact between condoctors 21, 22. The spring 55 assists in maintaining the brush 51 in the radially inward or closed position so that, when master switch 25 is initially closed, the switch assembly supplies current to the starting stator winding 12. As the speed of rotor shaft 15, sleeve 30, pin e, brush 51, spring 55 and cup-shaped shield 56 increases, the centrifugal force acting against spring 55 ultimately causes brush 51 to move outwardly to substantially the position shown in FIGURE 4. In so doing, permanent magnet 54 engages the inner end of cup-shaped shield 56 and assists in maintaining the brush 51 in outward or inoperative position.

The attraction of magnet 54 to the cup-shaped shield 56 prevents undesirable vibration of brush 51 during normal speed operation of the motor 10 and also during fluctuation in the speed of the motor which may result from varying loads being applied to the motor shaft 15. Magnet 54 should preferably be of such strength as to overcome approximately one-fourth of the pressure of spring 55 so that rotor shaft 15 may slow down to a speed less than that originally required to throw outwardly the brush 51 before the brush 51 will be urged back to the starting or closed position shown in FIGURE 3.

By way of example, spring 55 and the weight of brush 51, insulation plate 53 and magnet 54 should be calculated so that a motor whose shaft 15 would rotate normally at a speed of 1150 revolutions per minute would cause the brush 51 to move radially and outwardly out of engagement with slip rings a, b when the speed of the shaft 15 would exceed from 850 to 1000 revolutions per minute. However, after the magnet 54 is moved into engagement with the shield 56, the shaft 15 of motor 10 would have to slow down to a speed of approximately 570 to 750 revolutions per minute before the strength of the spring 55 would become effective to overcome the strength of the magnetic field of magnet 54 and return bushing 51 to the closed position shown in FIGURE 3.

In the instance of a motor whose rotor shaft 15 is to normally rotate at 1800 revolutions per minute it may be desirable to choose the spring 55 so that brush 51, insulating plate 53 and magnet 54 will move outwardly, following the starting of the motor 10, upon the speed of rotor shaft 15 and sleeve 30 reaching from 1400 to 1600 revolutions per minute. Here again, the strength of the magnetic field of magnet 54 should then be such that the magnetic field will be overcome by spring 55 when the speed of rotor shaft 15 would drop to approximately 1140 to 1200 revolutions per minute.

It is thus seen that I have provided an improved centrifugal switch assembly having stationary metallic slip rings within which a rotary part may freely rotate, and wherein a brush extending between the slip rings may normally engage the same while rotating with the rotary part and, upon the speed of the rotary part accelerating to a predetermined minimum speed following the starting thereof, the brush will move outwardly away from the slip rings to break the electrical contact therebetween. It is also seen that I have provided means completely enclosing the switch segment or brush and the stationary slip rings so as to prevent dirt, moisture and the like from getting onto the most important operating parts of the centrifugal switch assembly, all of which contributes greatly to prolonging the useful life of the switch assembly.

In the drawings and specification there has been set forth a preferred embodiment of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claim.

I claim:

A centrifugal switch assembly comprising (a) a rotatable sleeve,

(b) a pair of axially spaced insulation rings journaled on said sleeve,

(0) a pair of slip rings fixed on :said insulation rings,

(d) a pin carried by and extending radially outwardly from a medial portion of said sleeve,

(e) a metallic brush loosely penetrated by said pin and adapted to engage said slip rings,

(f) a compression spring encircling said pin and normally urging said brush inwardly into engagement with said slip rings,

(g) said brush being adapted to move outwardly to inoperative position in opposition to said compression spring upon rotation of said sleeve, said pin and said brush above a predetermined minimum speed for (j) the strength of said magnet being less than the opbrcaking the contact between said slip rings, posing force applied thereto by said spring so that said (h) a substantially cup-shaped metallic shield spaced p g Will Overcome the Strength of Said magnet outwardly fro id b h h id b h i engagwhen the speed of rotation of said sleeve is reduced ing said slip rings and carried by the outer portion of 5 to a predetermined maximum speed to return the said pin and being of a depth sufficient to completely to closed Position in engagement with Said receive said compression spring therein, slip rings.

(i) a permanent magnet secured in fixed relation to the outer surface of said brush and normally spaced in- References Clted by the Exammer wardly from said cup-shaped shield, whereby, upon 10 UNITED STATES PATENTS centrifugal force forcing said brush outwardly and 2,374,986 5/45 Fetter 20067 X causing said permanent magnet to engage said cup- 2,833,879 5/58 Naul 200-80 shaped shield, due to acceleration in the speed of said 2,868,917 1/59 Maerker 200-80 sleeve, the magnet will assist the centrifugal force in 15 maintaining said brush in said inoperative position, BERNARD GILHEANY Plmary Exammer' and ROBERT K. SCI-IAEFER, Examiner. 

